Mercruiser 120 seized up

[Pamela1217]

I just recently bought this boat it is a 1989 Glasstream the boat itself is in good shape. But the motor is seized up I knew this when I bought it I got it cheap. I have already pulled their stern drive and it is working good. I have poured miracle oil down all the spark plugs and now letting it sit for a week. My question is can I completely disassemble the front engine mount so I can access the front of the crank to put a breaker bar on it. It will not be hard to support the front of the motor but this will mean I will have to completely removed the mount from the boat. I thought I would try this before completely pull the motor. And does anybody know where I can get a service manual for this motor I have checked local dealers and nobody has it.

 

[markrob76]

Re: Mercruiser 120 seized up

I have a 79 120 cruiser and just got it running yes you can take the front mount off after supporting front of motor. I used my car engine hoist to do this. The problem I found that there was no center bolt to put on a socket so I used a tool that I have for holding water pump pulley by the bolts for a ford truck with the screw on fan they sell them at napa but check to see if oreilys auto rents it. hope you get it to turn over.

ps hook tool on bolts of crank pulley

 

[Pamela1217]

Re: Mercruiser 120 seized up

Thanks I have got it free up starter was weak now getting it rebuilt. I am having trouble with the silver light shifter can not find any information on how it works. It will not engage drive also any suggestions on a good oil to put in now that it is free.

 

[Pamela1217]

Re: Mercruiser 120 seized up

Sorry its a quick silver shifter

 

[couvmerk123]

Re: Mercruiser 120 seized up

Your glassstream probably has the same shifter that mine came with (91 with 3.0). Mine needed to be taken apart and after a good cleaning and marine grease it is smooth as butter. It felt just like bad cables which is what I originally expected. Will it move if you press the throttle button in ?

 

[Pamela1217]

Re: Mercruiser 120 seized up

Will not shift at all I will try to pull it apart and clean it up. I just to do it with out anything to go by

 

[markrob76]

Re: Mercruiser 120 seized up

Will not shift at all I will try to pull it apart and clean it up. I just to do it with out anything to go by

Pamela, check to make sure that the linkage for the lower unit on the stern drive is lined up properly this will cause a bind on the linkage and won't work the way it should. As far as motor oil I use a straight 30 weight and I found out the filter is cheaper by using a automotive on the oil filter number is a PF 25 AC or Fram it also takes 4 quarts to fill with new filter but make sure to check it for leaks and proper oil level after running the motor. The manual I got with my boat is a Clymer's Mercruiser stern drive shop manual 1964-1985 manual book number is B740. I would try ebay and see if you could find one. It has good pictures of thing plus good wiring diagrams. but some things could be covered better in it but it gets you in the ballpark if you know what I mean. hope this info helps you out and gets you on the water.

P.S.
If you need parts try boatingbuddy.com I found that they have great pricing and are very helpful.
Good Luck
Markrob76

 

[Pamela1217]

Re: Mercruiser 120 seized up

Ok here is an up dat I have moter free up and have change oil and all the plugs. But the motor will not start It is getting fire and I have even try putting gas down the carb with no luck. I have check fireing order and it is getting gas to carb.

 

[Bondo]

Re: Mercruiser 120 seized up

Ok here is an up dat I have moter free up and have change oil and all the plugs. But the motor will not start It is getting fire and I have even try putting gas down the carb with no luck. I have check fireing order and it is getting gas to carb.

Ayuh,... What's it's Compression numbers,..??

 

[markrob76]

Re: Mercruiser 120 seized up

Hey Pamela,
This sounds so familiar just went through this myself. check the compression on all cylinders by using a automotive compression gauge go to Oreily's and rent one from them to use. now pull all the plugs out put gauge in each cylinder and turn motor over three revolutions and record how much pressure you have. Do this again but put some oil down each cylinder about a couple of tablespoons and turn over a couple of times and repeat the compression test. The first test reading should be around 120 to 165 lbs. email me any qestions at markrob76@ymail.com

 

[Pamela1217]

Re: Mercruiser 120 seized up

Here is co,pression reading
1- 100
2- 95
3- 105
4- 100

After putting oil in
1- 170
2- 190
3- 160
4- 165

Now keep in mind that it was seized up not real bad. I did not want to force it so I soak each cylender before I tryed to trun it over. Then after it freed up I took it very slow and turn it over a few time before I tryed it with the start. I know 90 is a little low but that might get better. The gas in it is about two years old but was treated with stabilizer before it was stored.

 

[Pamela1217]

Re: Mercruiser 120 seized up

Ok been messing with this boat must of the day drained old gas out new gas in. But I went back and recheck cylender presure with out oil in cylenders

1 -120
2- 90
3- 90
4- 90

 

[markrob76]

Re: Mercruiser 120 seized up

I would say that the compression numbers aren't that bad for a motor that was seized up. Good thing to get the old gas out and put in fresh. What color is the spark? Use a old or new spark plug hook it to any plug wire and lay it on a good ground on the motor have someone turn it over and see what color you have. orange to red spark is weak and blue to white is strong. Also did you check your fuel pressure to the carb and did you replace the fuel filters? The thing almost everyone forgets is do the basics first so you know what you have. compression spark and fuel. as long as you have those three things the motor should run. After that then start to do your trouble shooting from there. Did you look to see if you could find a service manual on ebay? If you can't find one go to the library and talk to one of the people there I bet they have one and it is in there reference section but you will have to use it there and make copies of the pages you need.

well hope this gets you closer to getting in the water.
markrob76

 

[Bondo]

Re: Mercruiser 120 seized up

Ok been messing with this boat must of the day drained old gas out new gas in. But I went back and recheck cylender presure with out oil in cylenders

1 -120
2- 90
3- 90
4- 90

Ayuh,.... Sorry Pam, that motor is a Rebuildable core, 'n Not a runnin' motor....

At under 100psi,... If it runs at all, it'll have Zer0 power, 'n many runability issues...

Call a Machine Shop for a rebuild quote, or buy yerself a long block replacement,....

That motor Ain't gonna push yer boat, Nowhere...

 

[markrob76]

Re: Mercruiser 120 seized up

the motor will be fine. Just give it a chance service manual on ebay item number271025568006